Project Summary According to UNAIDS, there were 36.9 million people around the world living with HIV and more than 1.8 million new infections that were diagnosed in 2017. The epidemic is not under control, and a significant growth of youth in developing countries will only compound the problem. Truvada, a pill composed of tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC), is the only drug approved for pre-exposure prophylaxis (PrEP) for men and wormen during high HIV risk activities. Adherence to the one pill per day regimen is crucial for significantly reducing potential HIV risk by sexual transmission. Therefore, monitoring drug levels in real time in the clinic would provide necessary interventions to support adherence, particularly during behavior or lifestyle changes. While pharmacokinetic approaches exist for measuring Truvada?s active drug metabolite, tenofovir (TFV), there is still no point-of-care test to measure TFV in HIV prevention or treatment regimens. Our project is aimed at filling this gap by developing and validating a novel aptamer-based biosensor, or aptasensor, capable of detecting tenofovir in various biological fluids, at the point-of-care/clinic, with a simple-to-use procedure, which will empower health care providers to provide real-time feedback with each prescription renewal. Aptamers are DNA or RNA-based ligands capable of binding specifically to small molecules. Because of their small size, stability, high specificity, and reproducibility, aptamers can be applied to biosensor platforms to create a compact and sensitive assay well-suited for point-of-care tests. Combining a technology generated by Base Pair and CONRAD?s expertise in the area of HIV prevention, we propose to develop and clinically validate an aptasensor for measuring TFV. In Specific Aim 1, the TFV- specific aptamer combined with a biosensor platform will be optimized and tested in TFV-spiked simulant and clinical samples. We will validate the apatasensor in a pilot clinical trial in women taking Truvada at high and low adherence treatment regimens in Specific Aim 2. This project will provide proof-of-concept for a TFV aptasensor that can be further validated as a point-of-care test for therapeutic drug and adherence monitoring. Ultimately, real-time monitoring of adherence will lead to better counselling, resulting in higher effectiveness, and greatly contribute to the global initiative to reduce new HIV infections to fewer than 500,000 by 2020.